ASP.Net/Language Basics/If Statement

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If else Demo (C#)

<%@ Page Language="C#" %>
<script runat="server">
    void page_Load()
    {
         if(Page.IsPostBack)
         {
             if(chkIsMember.Checked==true){
                 lblOut.Text = "Members get a free ticket";
                 lblOut.BackColor=System.Drawing.Color.LightPink;
             }
             else if(Convert.ToInt32(txtAge.Text)<=18) {
                 lblOut.Text = "Students get a free ticket";
                 lblOut.BackColor=System.Drawing.Color.LightPink;
             }else {
                 lblOut.Text = "Price is 500";
                 lblOut.BackColor=System.Drawing.Color.LightSeaGreen;
             }
         }
    }
</script>
<html>
<head>
</head>
<body>
    <br />
    <form runat="server">
        Please enter your age 
        <asp:TextBox id="txtAge" runat="server"></asp:TextBox>
        <br />
        Are you a member? 
        <asp:CheckBox id="chkIsMember" runat="server"></asp:CheckBox>
        <asp:Button id="Button1" runat="server" Text="Submit"></asp:Button>
        <br />
        <asp:Label id="lblOut" runat="server"></asp:Label>
        <br />
    </form>
</body>
</html>



If statement the check the input value from asp:TextBox (VB.net)

<%@ Page Language="VB" %>
<script runat="server">
    Sub Reset()
    
      Textbox1.Text = ""
      Textbox2.Text = "0"
    
    End Sub
    
    Sub Page_Load(sender As Object, e As EventArgs)
    
      If Not Page.IsPostback
        Reset()
      End If
    
    End Sub
    
    Sub btnSubmit_Click(sender As Object, e As EventArgs)
    
      If cint(textbox2.text) < 20 Then
    
        label1.text = "Hi " & textbox1.text & ", you are " & textbox2.text & ", which is young!"
    
      Else If cint(textbox2.text) < 40 Then
      
        label1.text = "Hi " & textbox1.text & ", you are " & textbox2.text & ", which means you"re middle-aged!"
    
      Else 
    
        label1.text = "Hi " & textbox1.text & ", you"re old!"
    
      End If
    
    End Sub
    
    Sub btnReset_Click(sender As Object, e As EventArgs)
    
      Reset()
    
    End Sub
</script>
<html>
<head>
</head>
<body>
    <form runat="server">
        <p>
            Enter your name: 
            <asp:TextBox id="TextBox1" runat="server"></asp:TextBox>
        </p>
        <p>
            Enter you age: 
            <asp:TextBox id="TextBox2" runat="server"></asp:TextBox>
        </p>
        <p>
            <asp:Button id="btnSubmit" onclick="btnSubmit_Click" runat="server" Text="Submit"></asp:Button>
            &nbsp; 
            <asp:Button id="btnReset" onclick="btnReset_Click" runat="server" Text="Reset"></asp:Button>
        </p>
        <p>
            <asp:Label id="Label1" runat="server"></asp:Label>
        </p>
    </form>
</body>
</html>



If then Demo (C#)

<script language="C#" runat="server"> 
void Page_Load()
{ 
  int intNumber, intGuess;
  Random r = new Random();
  intNumber = Convert.ToInt32(r.Next(10)) + 1;
  if (Page.IsPostBack) {
    intGuess = Convert.ToInt32(Guess.SelectedItem.Value);
   
    if (intGuess > intNumber) {
       Message.Text = "<BR><BR>Guess is too high<BR>Try again, it was " 
       + intNumber;
    }
    if (intGuess < intNumber) {
       Message.Text = "<BR><BR>Guess is too low<BR>Try again, it was " 
       + intNumber;
    }
    if (intGuess == intNumber) {
       Message.Text = "<BR><BR>Guess is correct!";
    }
  }
}
</script>
<html>
<head></head>
<body>
<form runat="server">
  Guess?
  <asp:dropdownlist id="Guess" runat="server">
    <asp:listitem>1</asp:listitem>
    <asp:listitem>2</asp:listitem>
    <asp:listitem>3</asp:listitem>
    <asp:listitem>4</asp:listitem>
    <asp:listitem>5</asp:listitem>
    <asp:listitem>6</asp:listitem>
    <asp:listitem>7</asp:listitem>
    <asp:listitem>8</asp:listitem>
    <asp:listitem>9</asp:listitem>
    <asp:listitem>10</asp:listitem>
 </asp:dropdownlist>
  <br>
  <br> 
  <input type="submit" value="Submit guess">
  <asp:label id="Message" runat="server"/>
</form>
</body>
</html>



Multiple conditions in If statement (VB.net)

<%@ Page Language="VB" %>
<script runat="server">
    Sub Calendar1_SelectionChanged(sender As Object, e As EventArgs)
      If Day (Calendar1.SelectedDate) = 13 And Calendar1.SelectedDate.DayOfWeek = 5 Then
        Label1.Text = "Careful! Friday 13th is an unlucky day for some people!"
      Else
        Label1.Text = "It"s just another day in life..."
      End If
    End Sub
</script>
<html>
<head>
</head>
<body>
    <form runat="server">
        <p>
            Please select a date:
        </p>
        <p>
            <asp:Calendar id="Calendar1" runat="server" OnSelectionChanged="Calendar1_SelectionChanged"></asp:Calendar>
        </p>
        <p>
            <asp:Label id="Label1" runat="server"></asp:Label>
        </p>
    </form>
</body>
</html>



Nested if statement (C#)

<script language="C#" runat="server"> 
void Page_Load()
{ 
  int intNumber, intGuess;
  Random r = new Random();
  intNumber = Convert.ToInt32(r.Next(10)) + 1;
  if (Page.IsPostBack) {
    intGuess = Convert.ToInt32(Guess.SelectedItem.Value);
   
    if (intGuess > intNumber) {
       Message.Text = "<BR><BR>Guess is too high<BR>Try again, it was " 
       + intNumber;
    }
    if (intGuess < intNumber) {
       Message.Text = "<BR><BR>Guess is too low<BR>Try again, it was " 
       + intNumber;
    }
    if (intGuess == intNumber) {
       Message.Text = "<BR><BR>Guess is correct!";
    }
  }
}
</script>
<html>
<head></head>
<body>
<form runat="server">
  What number am I thinking of?
  <asp:dropdownlist id="Guess" runat="server">
    <asp:listitem>1</asp:listitem>
    <asp:listitem>2</asp:listitem>
    <asp:listitem>3</asp:listitem>
    <asp:listitem>4</asp:listitem>
    <asp:listitem>5</asp:listitem>
    <asp:listitem>6</asp:listitem>
    <asp:listitem>7</asp:listitem>
    <asp:listitem>8</asp:listitem>
    <asp:listitem>9</asp:listitem>
    <asp:listitem>10</asp:listitem>
 </asp:dropdownlist>
  <br>
  <br> 
  <input type="submit" value="Submit guess">
  <asp:label id="Message" runat="server"/>
</form>
</body>
</html>



Nested if statement (VB.net)

<script language="vb" runat="server"> 
Sub Page_Load()
  Dim theNumber As Integer
  Dim theGuess As Integer
  theNumber = int(10 * rnd) + 1
  If Page.IsPostBack Then
    theGuess = Guess.SelectedItem.Value
    If theGuess > theNumber then
      Message.Text = "<BR><BR>Guess is too high<BR>Try again ?it was " _
      & theNumber
    End If
    If theGuess < theNumber then
      Message.Text = "<BR><BR>Guess is too low<BR>Try again ?it was " _
      & theNumber
    End If
    If theGuess = theNumber then
      Message.Text = "<BR><BR>Guess is correct!"
    End If
  End If
End Sub
</script>
<html>
<head></head>
<body>
<form runat="server">
  What number am I thinking of?
  <asp:dropdownlist id="Guess" runat="server">
    <asp:listitem>1</asp:listitem>
    <asp:listitem>2</asp:listitem>
    <asp:listitem>3</asp:listitem>
    <asp:listitem>4</asp:listitem>
    <asp:listitem>5</asp:listitem>
    <asp:listitem>6</asp:listitem>
    <asp:listitem>7</asp:listitem>
    <asp:listitem>8</asp:listitem>
    <asp:listitem>9</asp:listitem>
    <asp:listitem>10</asp:listitem>
  </asp:dropdownlist>
  <br>
  <br> 
  <input type="submit" value="Submit guess">
  <asp:label id="message" runat="server"/>
</form>
</body>
</html>
Источник — «http://nfex.ru/index.php?title=ASP.Net/Language_Basics/If_Statement&oldid=2206»